Most timing constraints analyses for embedded systems are based on task level timing parameters whereas initial timing constraints are usually observed and specified with respect to visible events. In this paper, we propose a rate assignment algorithm for embedded reactive real-time systems whose timing constraints are specified by the rate of external input events. The rates of internal events which propagate through reactive chains are derived by the analysis of behavioral specification of each task. Then from the results we determine the rates of tasks. We present a case study which shows that the proposed approach allows more efficient design of embedded reactive real-time systems.